#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>

int main()
{
    int n = 0;
    scanf("%d", &n);
    int sign = 1;
    int m = 0;
    double sum = 0.0;
    int i = 0;
    for (i = 1; i <= n; i++)
    {
        m += (sign * (2 * i - 1));
        sum += 1.0 / m;
        sign *= -1;
    }
    printf("%.3lf\n", sum);
    return 0;
}